Electric batteries

ABSTRACT

The present invention relates to an electric battery ( 10 ). The electric battery ( 10 ) comprises plural battery cells ( 12 ), with each battery cell comprising a container. The container contains an electrochemical arrangement. Each battery cell ( 12 ) comprises positive and negative terminals of sheet form which extend from the electrochemical arrangement. The electric battery further comprises plural measurement arrangements ( 14 ), with each of the plural measurement arrangements being electrically coupled to each of two spaced apart locations on one of the positive and negative terminals of a respective one of the plural battery cells. Each of the plural measurement arrangements ( 14 ) is configured to measure potential difference between the two spaced apart locations.

FIELD OF THE INVENTION

The present invention relates to an electric battery configured tomeasure current sourced from or sunk by the electric battery and moreparticularly but not exclusively to an electric battery comprisingplural battery cells, the electric battery being configured to measurecurrent sourced from or sunk by each of at least one of the pluralbattery cells.

BACKGROUND ART

Lithium-ion battery cells have seen widespread use in small consumerdevices such as laptop computers and mobile telephones. Lithium-ionbatteries have recently begun to supplant conventional batteries inapplications having greater electrical energy demands, such aselectrical vehicles and static electricity generation apparatus.Lithium-ion batteries are seeing increased use on account of theirnormally superior performance over conventional batteries, such aslead-acid and NiMH batteries, in particular in respect of energy storagedensity and power density. To meet electrical energy demand in suchlarger energy demand applications a battery is typically comprised ofplural lithium-ion battery cells which are arranged in at least one ofseries and parallel depending on current and voltage requirements.Lithium-ion batteries can be dangerous under certain conditions onaccount of their containing flammable material. Safe and effective useof a lithium-ion battery normally requires operation of the batterywithin its Safe Operating Area (SOA). Considering operation within a SOAfurther, most lithium-ion cells can be damaged if discharged below acertain voltage or if charged or discharged at too high a current. Inaddition there is often the lesser constraint of a Normal Operating Area(NOA). Breaching the NOA can result in reduction in capacity or celllife over time. These challenges are compounded by the multi-cellconfiguration of the typical lithium-ion battery wherein unevenness ofthe state of charge can arise between cells. Careful management by wayof a battery management system (BMS) is therefore normally required toprovide for safe and effective operation.

Battery management systems for lithium-ion battery arrangements areknown. Such a battery management system typically makes measurements ofproperties such as current, voltage and temperature in a battery andmakes determinations concerning safe and effective operation based onthe measurements. Where current is measured either a discrete senseresistor or a Hall Effect device is used.

The present inventors have become appreciative of shortcomings in knownapproaches to measurement of current sourced from or sunk by electricbatteries. The present invention has been devised in light of theinventors' appreciation of such shortcomings. It is therefore an objectfor the present invention to provide an electric battery comprisingplural battery cells and a measurement arrangement configured to providefor measurement of current sourced from or sunk by each of at least oneof the plural battery cells.

STATEMENT OF INVENTION

According to a first aspect of the present invention there is providedan electric battery comprising:

-   -   plural battery cells, each battery cell comprising a container,        which contains an electrochemical arrangement, and positive and        negative terminals of sheet form extending from the        electrochemical arrangement; and    -   plural measurement arrangements, each of the plural measurement        arrangements being electrically coupled to each of two spaced        apart locations on one of the positive and negative terminals of        a respective one of the plural battery cells, the measurement        arrangement being configured to measure potential difference        between the two spaced apart locations.

The electric battery comprises plural battery cells. Each of the pluralbattery cells comprises a container. The container contains anelectrochemical arrangement. The container may be sealed. Theelectrochemical arrangement may be operative to generate electricalenergy from chemical reaction. Positive and negative terminals of sheetform extend from the electrochemical arrangement. The electric batteryfurther comprises plural measurement arrangements, each of the pluralmeasurement arrangements being electrically coupled to each of twospaced apart locations on one of the positive and negative terminals ofa respective one of the plural battery cells. The measurementarrangement is configured to measure potential difference between thetwo spaced apart locations.

Measurement of potential difference between the two spaced apartlocations may provide for determination of current passing between thetwo spaced apart locations and hence current sourced from or sunk by thebattery cell. Current may be sourced from the battery cell when thebattery cell is operative, perhaps along with the other battery cells,to provide electrical power. Current may be sunk by the battery cellwhen the battery cell is being charged.

The current passing between the two spaced apart locations may bedetermined in dependence on the measured potential difference and aresistance between the two spaced apart locations. The terminal of theelectric battery may therefore be operative as a parasitic resistancewhereby no additional sense resistance, such as a discrete resistor, isrequired to sense current flowing from or to the battery cell. Thecurrent may be determined in dependence on Ohm's Law such that I=V/R,where V is the measured potential difference and R is the resistancebetween the two spaced apart locations.

The resistance between the two spaced apart locations may bepredetermined. The resistance may be determined in dependence on atleast one of a material property of the terminal and dimensions of theterminal. The material property of the terminal may be bulk resistivity,p, of the terminal. The dimensions of the terminal may comprise lengthof the terminal, width of the terminal and thickness of the terminal.More specifically the dimensions of the terminal may be expressed asL/(t·W), where L is length, t is thickness and W is width. Theresistance may be predetermined on the basis of R=(ρ·L)/(t·W). Theresistance may be predetermined before use of the electrical batterysuch as during a calibration phase. The predetermined resistance may bestored in data storage. The data storage may be comprised in themeasurement arrangement.

Bulk resistivity, ρ, varies with temperature. Often the temperature ofthe terminal varies to an extent sufficient to merit taking variation ofbulk resistivity with temperature into account. The electric battery maytherefore comprise a temperature sensor disposed so as to sensetemperature in the vicinity of the terminal. The measurement arrangementmay be configured to adjust bulk resistivity, ρ, for sensed temperature.More specifically the measurement arrangement may comprise a look uptable of bulk resistivity, ρ, against temperature. The look up table maybe stored in data storage. The electric battery may comprise pluraltemperature sensors, each of the plural temperature sensors beingdisposed so as to sense temperature in the vicinity of a terminal of arespective one of the plural battery cells.

For a terminal of given width and thickness the measurement arrangementmay be coupled to the terminal at two locations which are spaced apartfrom each other by a predetermined amount to thereby establish a lengthof resistance of the terminal between the two locations whereby theresistance of the terminal between the two locations is predetermined.It may be desirable to have a smaller separation between the twolocations than is afforded by the given dimensions of the terminal. Thisissue may be addressed if at least one of the width and the thickness ofthe terminal is reduced by a corresponding amount. Reduction in widthmay be more practical than reduction in width. The terminal maytherefore be of non-uniform width. More specifically the terminal may benarrower between the two spaced apart locations than at the two spacedapart locations or on each side of the two spaced apart locations.

An electric battery may comprise first and second bus bars to which thepositive and negative terminals of the plural battery cells areelectrically connected. The electric battery may be configured such thatone of the two locations at which the measurement arrangement iselectrically coupled to the terminal is a bus bar and more specificallyone of the first and second bus bars.

Each of the positive and negative terminals may comprise conductivemetal such as copper, nickel or aluminium. Each of the positive andnegative terminals may have the form of a foil. A proximal end of eachof the positive and negative terminals may extend from theelectrochemical arrangement. A proximal end of each of the positive andnegative terminals may be electrically coupled, such as by way ofwelding, to a respective one of the electrodes of the electrochemicalarrangement. The measurement arrangement may be contained at least inpart within the container. Where the container is sealed, the batterycell may be configured such that each of the positive and negativeterminals extends from its respective electrode to outside the containerwithout compromising the seal formed by the container.

The potential difference between the two spaced apart locations may beof the order of mV. The measurement arrangement may therefore comprisean amplifier which is electrically coupled to the two spaced apartlocations and is configured to amplify the potential difference betweenthe two spaced apart locations. More specifically the amplifier may be adifferential amplifier. The measurement arrangement may also comprise afilter and more specifically a low pass filter. A desired resistancebetween the two spaced apart locations may not depend alone on theconfiguration and material characteristics of the terminal or the desireto minimise resistance and thereby reduce power dissipation. A furtherfactor may be a characteristic of an amplifier operative to amplify asignal, such as potential difference, measured at the spaced apartlocations. A lower gain amplifier may require a larger resistancebetween the spaced apart locations which increases power dissipation. Onthe other hand, a higher gain amplifier reduces resistance between thespaced apart locations whilst increasing amplification of noise andthereby degrading quality of measurement. There may therefore be acompromise involved in respect of determining resistance between thespaced apart locations.

The electric battery may comprise plural sets of battery cells, each setof battery cells comprising plural battery cells. More specifically eachset of battery cells may comprise a measurement arrangement, the pluralbattery cells within a set of battery cells being connected to eachother in parallel. Connecting the plural battery cells within a set inparallel causes the resistance of their cell terminals to be seen inparallel whereby the combined resistance of the terminals is reduced bythe inverse of the number of battery cells in parallel. The measurementarrangement may be configured such that the potential difference acrossthe combined resistance is measured.

A battery cell may comprise two measurement arrangements with each ofthe two measurement arrangements being electrically coupled to each oftwo spaced apart locations on a respective one of the positive andnegative terminals of the battery cell. Current may thus be measured ineach of the positive and negative terminals of the battery cell wherebyredundancy of current measurement may achieved in view of the currentflowing in the positive and negative terminals being substantially thesame.

The measurement arrangement may comprise an analogue to digitalconverter. The measurement arrangement may be configured such that theanalogue to digital converter is operative to convert measured potentialdifference from analogue form to digital form.

The measurement arrangement may comprise a processor such as amicroprocessor which is configured to process the measured potentialdifference. The processor may be configured to convert the measuredpotential difference to measured current. The measurement arrangementmay be further configured to measure cell voltage. More specifically themeasurement arrangement may comprise a cell voltage amplifier such as adifferential amplifier which is operative to measure a potentialdifference between positive and negative terminals of the battery cell.The processor may be operative to receive an output from the cellvoltage amplifier and to process the output. Where the electric batterycomprises a temperature sensor, the processor may be operative toreceive an output from the temperature sensor and to process the output.

The measurement arrangement may further comprise a communicationscircuit which is configured to at least one of provide data to andreceive data from the measurement arrangement. The electric battery maybe configured such that the communications circuit is operative toconvey at least one of data to and data from elsewhere such as asupervisory processor comprised in the electric battery or a measurementarrangement comprised in another battery cell.

The measurement arrangement may be unitary with the battery cell. Theelectric battery may comprise a circuit board, such as a printed circuitboard, comprising the measurement arrangement. The circuit board may bemechanically coupled to the battery cell such that the measurementarrangement couples electrically to the two spaced apart locations onthe terminal. The terminal may be attached, such as by way of bonding orclamping, to the circuit board.

The electric battery may comprise a carrier which is configured tosupport the battery cell. As mentioned above, the measurementarrangement may be unitary with the battery cell. The carrier maycomprise the measurement arrangement whereby the measurement arrangementis unitary with the battery cell and its carrier. The carrier may havethe form of a printed circuit board. Battery cells may vary in respectof form factor from manufacturer to manufacturer. The carrier maytherefore be configured for a battery cell of particular form factor.The measurement arrangement may be of the same form irrespective of thebattery cell. Accordingly the measurement arrangement may be mounted onthe carrier.

The battery cell may comprise at least one pouch cell. The container maytherefore contain one or more pouch cells. Where the container comprisesplural pouch cells such that a battery cell is, for example, ofprismatic form the positive and negative terminals may be common to theplural pouch cells. A pouch cell may comprise an electrochemicalarrangement which is contained within a pouch cell container and morespecifically a sealed pouch cell container which may be pliable wherebyswelling of the pouch cell container may be allowed for. Theelectrochemical arrangement may comprise a lithium-ion electrochemicalarrangement and more specifically a lithium-ion polymer electrochemicalarrangement. The positive and negative terminals may extend from thesame end of the electrochemical arrangement. Alternatively the positiveand negative terminals may extend from different ends of theelectrochemical arrangement and more specifically opposite ends of theelectrochemical arrangement.

The present inventors have appreciated that the feature of the circuitboard comprising the measurement arrangement may be of widerapplicability than hitherto described. Therefore and according to asecond aspect of the present invention there is provided an electricbattery comprising:

-   -   plural battery cells, each battery cell comprising a container,        which contains an electrochemical arrangement, and positive and        negative terminals of sheet form extending from the        electrochemical arrangement; and    -   plural circuit boards each comprising an electrical conductor        and a measurement arrangement, each of the plural circuit boards        being configured and disposed relative to one of the positive        and negative terminals of a respective one of the plural battery        cells such that electric current passing through the terminal of        the battery cell passes through the electrical conductor, the        measurement arrangement being electrically coupled to each of        two spaced apart locations on the electrical conductor, the        measurement arrangement being configured to measure potential        difference between the two spaced apart locations.

The electric battery comprises plural battery cells. Each battery cellcomprises a container, which contains an electrochemical arrangement,and positive and negative terminals of sheet form extending from theelectrochemical arrangement. The electric battery further comprisesplural circuit boards. Each of the plural circuit boards comprises anelectrical conductor and a measurement arrangement. The circuit boardmay comprise a printed circuit board, the printed circuit board definingthe electrical conductor. Each of the plural circuit boards isconfigured and disposed relative to one of the positive and negativeterminals of a respective one of the plural battery cells such thatelectric current passing through the terminal of the battery cell passesthrough the electrical conductor. The measurement arrangement iselectrically coupled to each of two spaced apart locations on theelectrical conductor. Furthermore the measurement arrangement isconfigured to measure potential difference between the two spaced apartlocations. Measurement of potential difference between the two spacedapart locations by each measurement arrangement provides fordetermination of current flowing between the two spaced apart locationsand hence current flowing from or to each of the plural battery cells.

The electric battery may further comprise at least one processorconfigured to receive an output from at least one measurementarrangement and to determine current passing between at least one pairof two spaced apart locations in dependence thereon. More specificallythe electric battery may comprise plural processors, each of the pluralprocessors being configured to determine current passing between arespective pair of spaced apart locations. Each of the plural processorsmay be comprised in and perhaps unitary with a respective one of theplural circuit boards. More specifically the processor may be mounted onthe circuit board.

The processor may be configured to determine current passing between thetwo spaced apart locations in dependence on the measured potentialdifference and resistance of the electrical conductor between the twospaced apart locations. The resistance of the electrical conductorbetween the two spaced apart locations may be predetermined. Theresistance of the electrical conductor between the two spaced apartlocations may depend on a material property of the electrical conductorand dimensions of the electrical conductor between the two spaced apartlocations such as separation between the two spaced apart locations,width of the electrical conductor and thickness of the electricalconductor. The resistance of the electrical conductor may be determinedbefore use of the electric battery such as during calibration. Thedetermined resistance may be stored in data storage comprised in themeasurement arrangement.

The circuit board may be attached to the battery cell whereby thecircuit board and the battery cell are unitary. The circuit board may bedisposed relative to the battery cell such that a distal end of theterminal is attached, such as by bonding or clamping, to the circuitboard whereby the electrical conductor is in series with the terminal.The distal end of the terminal may constitute one of the two spacedapart locations between which potential difference is measured by themeasurement arrangement.

As described above with reference to the first aspect of the presentinvention the processor may be further configured to at least one of:measure cell voltage; and receive a temperature output from atemperature sensor comprised in the electric battery and to process thetemperature output. Alternatively or in addition and as described abovethe measurement arrangement may further comprise a communicationscircuit which is configured to at least one of provide data to andreceive data from the measurement arrangement.

Further embodiments of the second aspect of the present invention maycomprise one or more features of the first aspect of the presentinvention.

According to a further aspect of the present invention there is providedan electric battery comprising: plural battery cells, each battery cellcomprising an electrochemical arrangement, and positive and negativeterminals electrically coupled to the electrochemical arrangement; andplural measurement arrangements, each of the plural measurementarrangements being electrically coupled to each of two spaced apartlocations on one of the positive and negative terminals of a respectiveone of the plural battery cells, the measurement arrangement beingconfigured to measure potential difference between the two spaced apartlocations.

Further embodiments of the further aspect of the present invention maycomprise one or more features of the first or second aspect of thepresent invention.

BRIEF DESCRIPTION OF DRAWINGS

Further features and advantages of the present invention will becomeapparent from the following specific description, which is given by wayof example only and with reference to the accompanying drawings, inwhich:

FIG. 1 is a block diagram representation of an electric batteryaccording to the present invention;

FIG. 2 is a representation of a pouch cell of known form;

FIG. 3A is a representation of a pouch cell with a measurementarrangement according to a first embodiment of the present invention;

FIG. 3B is a representation of a pouch cell with a measurementarrangement according to a second embodiment of the present invention;

FIG. 4A is a representation in profile of the second embodiment of thepresent invention;

FIG. 4B is a representation in profile of plural pouch cells accordingto a third embodiment of the present invention;

FIG. 5 is a representation of a pouch cell with a measurementarrangement according to a fourth embodiment of the present invention inwhich a terminal of the pouch cell is used as a sense resistor;

FIG. 6 is a representation of a pouch cell with a measurementarrangement according to a fifth embodiment of the present invention inwhich a printed circuit board conductor is used as a sense resistor; and

FIG. 7 is a representation of a pouch cell of different configurationwith a measurement arrangement according to a sixth embodiment of thepresent invention.

DESCRIPTION OF EMBODIMENTS

A block diagram representation of an electric battery 10 according tothe present invention is shown in FIG. 1. The electric battery comprisesplural lithium-ion polymer pouch cells 12 (each of which constitutes abattery cell) which are of conventional form and function except asdescribed herein. In another form, a battery cell is constituted byplural pouch cells, as described below with reference to FIG. 4B, whichare contained within a container whereby the battery cells is, forexample, of prismatic form. As is described in more detail below theelectric battery 10 comprises a parasitic resistor for each pouch cell12. Furthermore and as shown in FIG. 1 the electric battery 10 comprisesa differential amplifier 14 for each pouch cell 12 which is operative toamplify a potential difference developed across its respective parasiticresistor. Although not shown in FIG. 1, the electric battery 10comprises a low pass filter for each pouch cell 12 which is operative tofilter signals from its respective differential amplifier 14. Theelectric battery 10 further comprises for each pouch cell 12 ananalogue-to-digital converter 16, a microprocessor 18 and acommunications circuit 20. The analogue-to-digital converter 16 isoperative to receive the amplified potential difference from thedifferential amplifier 14 and to convert the amplified potentialdifference to digital form. The output from the analogue-to-digitalconverter 16 is then received in the microprocessor 18. As describedbelow in more detail the microprocessor 18 is operative to convert thereceived digital signal to a current value.

Although not shown in FIG. 1, a temperature sensor, such as athermocouple or resistance temperature detector (RTD), is disposed nearthe parasitic resistance of each pouch cell 12. The sensed temperatureis subject to signal conditioning, analogue to digital conversion andprocessing in the microprocessor 18. Although not shown in FIG. 1, thecell voltage of each pouch cell 12 is determined by way of a furtherdifferential amplifier which is operative to measure a potentialdifference between positive and negative terminals of the pouch cell.The measured cell voltage is subject to signal conditioning, analogue todigital conversion and processing in the microprocessor 18. The electricbattery 10 further comprises a communications circuit 20 which isoperative to receive pouch cell condition data from the microprocessor18. The pouch cell condition data includes current sourced from or sunkby the pouch cell, the pouch cell voltage and the temperature of thepouch cell. The communications circuit 20 is operative to convey thepouch cell condition data elsewhere. According to a first example thecommunications circuit 20 is operative to convey the pouch cellcondition data to the microprocessor 18 of another pouch cell 12.According to a second example the communications circuit 20 is operativeto convey the pouch cell condition data to a supervisory microprocessor22 comprised in the electric battery 10. According to a third example,the communications circuit 20 is operative to convey the pouch cellcondition data externally to the electric battery 10 such as to a remotemonitoring facility. The communications circuit 20 is also operative toreceive condition data from other communications circuits 20 and controldata from the supervisory microprocessor 22 or from the like of theremote monitoring facility.

A representation of a pouch cell 30 of known form is shown in FIG. 2.The pouch cell 30 is of known form and function and comprises a sealedpliable bag 32 (which constitutes a pouch cell container) containing alithium-ion polymer electrochemical arrangement which is operative togenerate electrical energy from chemical reaction. The pouch cell 30further comprises a positive terminal 34 and a negative terminal 36which extend from inside the pliable bag to outside the pliable bagwithout compromising the seal formed by the pliable bag. The proximal,i.e. internal, end of each positive and negative terminal iselectrically coupled to a respective electrode of the electrochemicalarrangement. Each positive and negative terminal is a foil formed fromcopper. In accordance with known practice the positive terminal 34 iselectrically connected to a first bus bar 38 and the negative terminal36 is electrically connected to a second bus bar 40.

A representation of a pouch cell with a measurement arrangementaccording to a first embodiment of the present invention is shown inFIG. 3A. The pouch cell of FIG. 3A is as per FIG. 2 in that it comprisesa pliable bag 52 which contains an electrochemical arrangement and fromwhich positive and negative terminals extend. For clarity ofillustration, only the positive terminal 34, 54 is shown in FIG. 3A. Thedifferential amplifier 14, 56 of FIG. 1 has two inputs. A first input 58to the differential amplifier 14, 56 is electrically connected to thepositive terminal 34, 54 near the pliable bag 52. A second input 60 tothe differential amplifier 14, 56 is electrically connected to theterminal 34, 54 near the first bus bar 38, 62. The connections made tothe positive terminal 34, 54 by the first and second inputs 58, 60 aretherefore spaced apart from each other by a distance L.

The length of positive terminal 34, 54 between the two connections 58,60 to the terminal constitutes a parasitic resistance across which apotential difference is developed and measured by the differentialamplifier 14, 56. The potential difference corresponds to currentpassing through the positive terminal, i.e. current sourced from or sunkby the pouch cell. To dissipate as little power as possible, it isdesirable for the resistance between the two connections to be very low,such as of the order of 200 μΩ. The resistance, R, between the twoconnections is given by R=(ρ·L)/(t·W) where ρ is the bulk resistivity ofthe terminal, L is the distance between the two connections, t is thethickness of the terminal and W is the width of the terminal. Here theterminal is formed of aluminium 0.1 mm thick. An aspect ratio of widthto length, i.e. W/L, of 1.37 is therefore required to provide aresistance of 200 μΩ. In the embodiment of FIG. 3A the spacing of thetwo connections is such that the terminal is too wide to achieve anaspect ratio of 1.37. Accordingly and as shown in FIG. 3A the width ofthe positive terminal 34, 54 is reduced 64 between the two connectionsto provide an aspect ratio of 1.37.

The bulk resistivity, ρ, of the terminal depends on temperature.Therefore the temperature sensor mentioned above is operative to sensethe temperature near the resistance defined between the two connectionsto the differential amplifier 14, 56. As mentioned above, the sensedtemperature is converted to digital form and received in themicroprocessor 18. During calibration the resistance defined between thetwo connections to the differential amplifier 14, 56 is determined andstored in data storage comprised in the microprocessor 18. Furthermorevariation in bulk resistivity, ρ, over temperature is stored in a lookup table. During use of the electric battery, the microprocessor 18 isoperative to determine the current sourced from or sunk by the pouchcell in dependence on the measured potential difference and the measuredtemperature. According to another calibration approach, a calibrationvalue is determined which converts the output from theanalogue-to-digital converter directly to current sourced from or sunkby the pouch cell. During use of the electric battery, the calibrationvalue is adjusted for variation in temperature as determined from thelook up table in dependence measured temperature. This approach providesfor calibration of the whole measurement and processing chain of FIG. 1.

A representation of a pouch cell with a measurement arrangementaccording to a second embodiment of the present invention is shown inFIG. 3B. Components in common with the first embodiment of FIG. 3A aredesignated with like reference numerals. The reader's attention isdirected to the description provided above with reference to FIG. 3A fora description of such common components. Features of the secondembodiment which differ from the first embodiment will now be described.As can be seen from FIG. 3B, the connection to the differentialamplifier 60 other than the connection closer to the pliable bag 52 iscombined with the first bus bar 62. This change in configurationprovides an increase in length of resistance whereby there is no need toreduce the width of the terminal 54 between the two connections to thedifferential amplifier 60.

A representation in profile of the second embodiment is shown in FIG.4A. Components in common with the second embodiment of FIG. 3B aredesignated with like reference numerals. The reader's attention isdirected to the description provided above with reference to FIG. 3B fora description of such common components.

A representation in profile of plural pouch cells according to a thirdembodiment of the present invention is shown in FIG. 4B. Components incommon with the second embodiment of FIG. 3B are designated with likereference numerals. The reader's attention is directed to thedescription provided above with reference to FIG. 3B for a descriptionof such common components. Features particular to the embodiment of FIG.4B will now be described. A cooling plate 72 is present between pairs ofadjacent pouch cells 52 and such that the adjacent pouch cells abutagainst and are supported by the cooling plate 72. In this embodiment abattery cell is constituted by the plural pouch cells 52 shown in FIG.4B. The positive terminals of the plural pouch cells 52 are electricallyconnected and the negative terminals of the plural pouch cells areelectrically connected whereby the pouch cells are connected inparallel. Measurement of current, voltage and temperature is in respectof each such parallel arrangement of pouch cells.

A representation of a pouch cell with a measurement arrangementaccording to a fourth embodiment of the present invention in which aterminal of the pouch cell is used as a sense resistor is shown in FIG.5. In the embodiment of FIG. 5 the positive 84 and negative 86 terminalswhich extend from the pliable bag 82 are bonded or clamped to a printedcircuit board 88 comprising the differential amplifier 90 and thefurther components comprised in the measurement and processing chain andsuch that the inputs to the differential amplifier 90 make an electricalconnection to the positive terminal 84 at spaced apart locations.

A representation of a pouch cell with a measurement arrangementaccording to a fifth embodiment of the present invention in which aprinted circuit board conductor is used as a sense resistor is shown inFIG. 6. Components in common with the fourth embodiment of FIG. 5 aredesignated with like reference numerals. The reader's attention isdirected to the description provided above with reference to FIG. 5 fora description of such common components. Features particular to theembodiment of FIG. 6 will now be described. The printed circuit board 88comprises a length of electrical conductor 92 which is operative as asense resistance instead of the positive terminal of the fourthembodiment. Furthermore the positive terminal 84 is clamped or bonded tothe printed circuit board 88 such that it makes electrical contact withone end of the length of electrical conductor 92. The other end of thelength of electrical conductor 92 is electrically connected to the firstbus bar 94. The length of electrical conductor 92 is therefore in seriesbetween the positive terminal 84 and the first bus bar 94. The printedcircuit board 88 is configured such that the two inputs to thedifferential amplifier 90 are electrically coupled to respective ends ofthe length of electrical conductor 92. The dimensions and materialproperties of the length of electrical conductor 92 determine theresistance seen by the differential amplifier 90.

A representation of a pouch cell of different configuration with ameasurement arrangement according to a sixth embodiment of the presentinvention is shown in FIG. 7. Components in common with the fifthembodiment of FIG. 6 are designated with like reference numerals. Thereader's attention is directed to the description provided above withreference to FIG. 6 for a description of such common components.Features particular to the embodiment of FIG. 7 will now be described.As can be seen from FIG. 7 the positive and negative terminals 84, 86extend from opposite sides of the pliable bag 82. The shape of theprinted circuit board 88 is configured accordingly whereby connection ofeach of the positive and negative terminals 84, 86 is to a respectiveone of two different arms of the printed circuit board 88.

The invention claimed is:
 1. An electric battery comprising: a pluralityof battery cells, each battery cell comprising a container, thecontainer containing an electrochemical arrangement, each battery cellfurther comprising positive and negative terminals of sheet formextending from the electrochemical arrangement; and a plurality ofmeasurement arrangements, each of the plurality of measurementarrangements: being electrically coupled to each of two spaced apartmeasurement locations on a same positive or negative terminal of arespective battery cell of the plurality of battery cells, and measuringa potential difference between the two measurement locations, wherebythe terminal constitutes a current sense resistor between the twomeasurement locations.
 2. The electric battery according to claim 1determining current passing between the two measurement locations independence on the measured potential difference and a resistance betweenthe two measurement locations.
 3. The electric battery according toclaim 2, wherein the resistance between the two measurement locations ispredetermined.
 4. The electric battery according to claim 3, wherein theresistance is predetermined in dependence on at least one of: a materialproperty of the terminal or dimensions of the terminal.
 5. The electricbattery according to claim 4, wherein the material property is bulkresistivity, ρ, of the terminal.
 6. The electric battery according toclaim 5, further comprising a temperature sensor disposed to sensetemperature in the vicinity of the terminal, the measurement arrangementadjusting bulk resistivity, ρ, in dependence on the temperature sensedwhen determining the current passing between the two measurementlocations.
 7. The electric battery according to claim 1, wherein theterminal is of predetermined width and thickness and the two measurementlocations are spaced apart from each other by a predetermined amount,whereby the resistance of the terminal between the two measurementlocations is predetermined.
 8. The electric battery according to claim7, wherein the terminal is of a non-uniform width whereby the terminalis narrower between the two measurement locations than at or on eachside of the two measurement locations.
 9. The electric battery accordingto claim 1, further comprising first and second bus bars to which thepositive and negative terminals of the plural battery cells areelectrically connected, wherein for each of the plurality of measurementarrangements, one of the two measurement locations at which themeasurement arrangement is electrically coupled to the terminal is oneof the first or second bus bars.
 10. The electric battery according toclaim 1, in which each of the positive and negative terminals has theform of a foil.
 11. The electric battery according to claim 1, in whicha proximal end of each of the positive and negative terminals iselectrically coupled to a respective electrode of the electrochemicalarrangement, each of the positive and negative terminals extending fromits respective electrode to outside the container without compromising aseal formed by the container.
 12. The electric battery according toclaim 1, comprising a plurality of sets of battery cells, each set ofbattery cells comprising a respective plurality of battery cellsconnected to each other in parallel, each set of battery cellscomprising one of the plurality of measurement arrangements, themeasurement arrangement of each set of battery cells measuring apotential difference across a combined resistance of terminals withinthe set of battery cells.
 13. The electric battery according to claim 1,wherein at least one battery cell of the plurality of battery cellscomprises two measurement arrangements with each of the two measurementarrangements being electrically coupled to each of two measurementlocations on a same respective positive or negative terminal of thebattery cell.
 14. The electric battery according to claim 1, whereineach of the plurality of measurement arrangements comprises an analogueto digital converter and a processor, the analogue to digital converterconverting measured potential difference from analogue form to digitalform and the processor converting the measured potential difference ofdigital form to measured current.
 15. The electric battery according toclaim 1, in which the measurement arrangement further measures batterycell voltage.
 16. The electric battery according to claim 1, whereineach of the plurality of measurement arrangements further comprises acommunications circuit which conveys at least one of data to and datafrom at least one of: a supervisory processor comprised in the electricbattery or a measurement arrangement comprised in another battery cell.17. The electric battery according to claim 1, in which the measurementarrangement is unitary with the battery cell.
 18. The electric batteryaccording to claim 1 comprising a circuit board, the circuit boardcomprising one of the plurality of measurement arrangements, the circuitboard being mechanically coupled to the battery cell such that themeasurement arrangement couples electrically to the two measurementlocations on the terminal.
 19. The electric battery according to claim 1comprising a carrier supporting the battery cell, the carrier comprisingone of the plurality of measurement arrangements, wherein the batterycell, the measurement arrangement, and the carrier are unitarily formed.20. The electric battery according to claim 1, in which a battery cellcomprises at least one pouch cell, each pouch cell comprising anelectrochemical arrangement.
 21. The electric battery according to claim1, in which the electrochemical arrangement comprises a lithium-ionpolymer electrochemical arrangement.
 22. The electric battery accordingto claim 1, wherein each measurement arrangement comprises an amplifierconfigured to measure the potential difference between the twomeasurement locations on the respective terminal and a filter configuredto filter signals from the amplifier.
 23. The electric battery accordingto claim 22, wherein the amplifier is a differential amplifier connectedto the two measurement locations on the terminal.
 24. The electricbattery according to claim 22, wherein the filter is a low pass filter.25. The electric battery according to claim 6, wherein the measurementarrangement comprises data storage storing a look up table of bulkresistivity, p, against temperature and the measurement arrangementadjusting the bulk resistivity, p, in dependence on the sensedtemperature using the look up table.